Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Atty Docket No. 99648
MOLD PIN AND MOLD FOR ITS USE
CROSS REFERENCES TO RELATED APPLICATIONS
This application is related to and claims priority from U.S. Provisional
Patent Application
No. 60/636,893, entitled: Mold Pin And Mold For Its Use, filed on December 17,
2004, and this
U.S. Provisional Patent Application is incorporated by reference herein.
FIELD OF THE INVENTION
The present invention is directed to rotational molding. In particular, the
present invention
is directed to pins used in rotational molds, and the molds, including their
castings.
BACKGROUND OF THE INVENTION
Rotational molding is a highly versatile manufacturing option. It allows for
unlimited
design possibilities with the added benefit of low production costs.
The rotational molding process starts with a good quality mold, that is
typically formed in
castings or halves, that define a mold cavity therein. The mold cavity is
configured to the
corresponding configuration of the desired component or product to be molded.
The castings are
placed together to form the mold, and the molds are placed into a molding
machine that has a
loading, heating, and cooling area.
Several molds, formed by the mold halves, may be placed on the machine at the
same time.
Pre-measured plastic resin is loaded into each mold, and then the molds are
moved into the oven
where they are slowly rotated on both the vertical and horizontal axis. The
melting resin sticks to
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the hot mold and coats every surface evenly. The mold continues to rotate
during the cooling cycle
so the parts retain an even wall thickness.
Once the parts are cooled, they are released from the mold. The rotational
speed, heating
times, and cooling times, are all controlled throughout the process.
Rotational molding offers design advantages over other molding processes. With
proper
design, parts that are assembled from several pieces can be molded as one
part, eliminating
expensive fabrication costs.
The rotational molding process also has a number of inherent design strengths.
These
strengths include, consistent wall thickness and strong outside corners, that
are virtually stress free.
If additional strength is required, reinforcing ribs can be designed into the
part.
Rotational molding delivers the product the designer envisions. Designers can
select the
best material for their application, including materials that meet
governmental requirements.
Additives to help make the part weather resistant, flame retardant, or static
free can be specified.
Inserts, threads, handles, minor undercuts, and flat surfaces, that eliminate
draft angles or
fine surface detail, can all be part of the design. Designers also have the
option of multi-wall
molding, that can be either hollow or foam filled.
Rotational molding is cost effective. Tooling is less expensive in comparison
to
conventional molding processes, such as injection molding and blow molding, as
an internal core is
not manufactured. By lacking an internal core, minor changes can be made to an
existing mold.
Moreover, since the components are formed with by heat, coupled with rotation,
as opposed to
pressure, as with injection and blow molding, a greater selection of
materials, including lightweight
materials can be used. Such lightweight materials are not possible for use
with the pressures of
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injection and blow molding, as these pressures limited these molding
operations to heavyweight
materials.
Fig. 1 A shows a casting 20 or half (also known as a mold tray) of a
conventional rotational
mold, having a depression 21, corresponding to a portion of the desired part
to be molded,
S impressed therein. The casting 20 is made of aluminum, and includes a boss
22 or elevated portion,
protruding from the depression 21, that supports a steel pin 24. The pin 24 is
a straight pin, utilized
in the mold to create bores or holes in the molded component or product. This
pin 24 extends from
the boss 22, initially in a straight orientation.
Fig. 1B shows a correspondingly configured mold casting 20' or half for use
with the mold
casting 20. The casting 20' also includes a depression 21', corresponding to
the portion of the
desired part to be molded. These two castings 20, 20', when placed together,
form the mold with a
mold cavity therein.
As shown in greater detail in Fig. 2, the pin 24 is received in a bore or hole
28 in the boss
22. The bottom portion 24a of the pin 24 is threaded along its exterior 30, to
be received by a nut
32, to hold the pin 24 in place. The boss 22 extends from the surface 20a of
the casting 20, for
example, to a height or longitudinal dimension indicated as "x". The upper
portion 24b of the pin
24 extends from the surface 22a of the boss 22.
While the castings 20, 20' make up a single mold, multiple castings 20, 20'
are provided on
racks 38, 38' respectively, as shown in Figs. 3A and 3B. When the racks 38,
38' are coupled to form
multiple molds, they are placed into a rotational mold apparatus or machine,
for producing
components or products in a single molding session.
However, this arrangement of the pin 24 in the casting 20 (in the boss 22)
exhibits
drawbacks. In particular, the pins 24 become bent or crooked over time. This
results in products
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that are unsatisfactory and must be rejected, The pins 24 become bent by
moving out of alignment,
in a relatively short time, as early as approximately 100 cycles. Accordingly,
after these
approximately 100 cycles, the pins 24 have to be manually straightened,
typically by being hit with
a hammer or mallet. This straightening technique cannot ensure straightening
of the pins 24, and
after the pins 24 have been hit too many times, they must be replaced.
Straightening or replacing
the pins 24 involves labor costs. Additionally, during periods of pin
straightening or replacement,
the molds are out of service. This results in lost production, and other
economic losses due to
production delays.
SUMMARY OF THE INVENTION
The present invention improves on the conventional art by providing a pin that
does not
require straightening over its usable life. It also provides a mold for use
with this pin. The pin
provides for increased heat transfer in the molding process. This increased
heat transfer inhibits
blow holes (also known as voids) from forming in the molded parts, such that
the molded parts,
resulting from the invention, include fewer, if any, blow holes, when compared
to parts formed in
conventional molds that use conventional mold pins. The pins also serves to
increase wall thickness
in the areas where they are located, also reducing the probability for blow
hole or void formation.
By reducing and eliminating conditions for blow hole formation, the rejection
rate of completed
parts is dramatically reduced.
As a result of this pin, mold production is more economical, as the number of
rejected
products is significantly reduced, and more products can be produced in a time
period. This is
because, the pins last longer than the conventional pins, and they do not
require maintenance over
their usable life. Moreover, the pins are releasable as a single unit, so that
when one needs to be
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replaced, it can be easily unscrewed from its holder and easily replaced with
another pin. The
replacement pin, upon its installation, will be in a straight alignment.
The mold pin of the invention is formed of a longitudinally extending rod-like
body with a
collar extending laterally or transversely from the body. The collar is of
peripheral and longitudinal
dimensions similar to those of a protrusion extending from the surface of a
mold tray (mold casting
or half), such that when the mold pin seats in the protrusion, the protrusion
and the collar define a
boss in the mold tray.
An embodiment of the invention is directed to a boss for a mold tray (mold
cavity or half),
that combined with another correspondingly configured mold tray defines a mold
cavity, in which
the part is formed. The boss is formed of a first portion and a second
portion. The first portion
extends from the surface of a portion of a mold tray. The second portion
includes a laterally
extending segment of a mold pin. The mold pin has a longitudinal body
supporting the laterally
extending segment, for example, a collar that journals the body, and at least
a portion of the
longitudinal body (e.g., in a cylindrical rod-like shape) is received in the
first portion of the boss.
Another embodiment of the invention is directed to a mold pin for receipt in a
mold tray
(mold casting or half). The mold pin has a longitudinally extending body of a
rod-like shape (e.g.,
cylindrical), and the body has a first end and a second end. A segment, for
example, a collar,
extends laterally from the body and is positioned along the body intermediate
the first end and the
second end. The laterally extending segment forms at least a portion of a boss
when the mold pin is
received in the mold tray.
Another embodiment of the invention is directed to a mold system. The mold
system
includes at least one mold tray (mold casting or half) having a portion
defining a portion of a mold
cavity. At least one protrusion extends from the portion defining the portion
of the mold cavity, and
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there is at least one mold pin. The mold pin has a longitudinally extending
rod-like shaped body
including a first portion and a second portion, and a laterally extending
segment, extending from the
body intermediate the first portion and the second portion. The second portion
is such that it is at
least temporarily received in the at least on protrusion. Additionally, the at
least one protrusion and
S the laterally extending segment define at least one boss in the mold tray.
BRIEF DESCRIPTION OF THE DRAWINGS
Attention is now directed to the drawing figures, where corresponding or like
components
are indicated by corresponding or like numbers or characters. In the drawings:
Fig. 1 A is a top view of the cavity side of a mold casting in accordance with
the
conventional art;
Fig. 1 B is a top view of the cavity side of a correspondingly configured mold
casting for the
mold casting of Fig. 1 A, in accordance with the conventional art;
Fig. 2 is a cross sectional view of the boss and pin taken along line 2-2 of
Fig. lA;
1 S Figs. 3A and 3B are top views of correspondingly configured mold castings
of Figs. 1 A and
1 B respectively, for placement into a rotational mold apparatus;
Fig. 4 is a top view of the cavity side of a mold casting with the pins and
bosses in
accordance with an embodiment of the invention;
Fig. 5 is a cross sectional view of the boss and pin taken along line S-S of
Fig. 4;
Fig. G is a perspective view of the pin in accordance with an embodiment of
the invention;
Fig. 7 is a view of the mold cavity formed by the casting of Fig. 4 with a
correspondingly
configured mold casting; and
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Fig. 8 is a perspective view of a product made from the mold castings in
accordance with the
embodiments of the present invention.
DETAILED DESCRIPTION
Fig. 4 shows an embodiment of the pin 40 of the present invention in a casting
42 or half
(mold tray), of a mold 43 (Fig. 7), for example, for a rotational molding
machine (apparatus). The
casting 42 includes a surface 42a that defines a depression 42d (similar to
depression 21 ),
corresponding to a portion of the desired part to be molded, impressed
therein. A protrusion 44
extends from the depression 42d in the casting 42, and its surfaces 44a and
44p (Fig. 5) are
continuous with the surface 42a. The protrusion 44 is, for example,
cylindrical in shape and of a
circular cross section. The protrusion 44 forms a part of a boss 45, as the
boss 45 is typically
formed from two parts. While multiple bosses 45, formed of pins 40 and
protrusions 44 are shown,
the molds 43 may use one or more boss 45, such that the pin 40 and protrusion
44 are representative
of all bosses 45, pins 40 and protrusions 44, in the mold 43.
1 S The other part of the boss 45 is formed by a laterally extending collar
segment or collar 46
of the pin 40. The pin 40 seats in the protrusion 44. This seating is such
that the pin 40, mainly at
its collar segment 46, is thermally coupled to the protrusion 44, and
typically, the protrusion 44 and
collar segment 46 of the pin 40 are in abutting contact. The pin 40, including
its collar segment or
collar 46, may be of a material with greater thermal conductivity than that of
the protrusion 44 and
the casting 42 (the casting 42 is an integral member including the protrusion
44), such that the pin
40 typically serves as a heat sink or the like.
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A bore 47 (Fig. 5) extends through the casting portion of the boss 45 for
receiving the pin
40, such that the pin 40 is in a "straight" orientation. The casting 42 is
similar to the casting 20
(detailed above) except for the boss 45, as detailed herein.
Turning also to Figs. 5 and 6, the pin 40 includes a collar 46, that extends
laterally
(transversely) from the pin body 54. The pin body 54 is, for example,
cylindrical and rod-like in
shape and of a circular cross-section, and it extends longitudinally (along
the longitudinal axis 55).
The pin body 54, at the collar 46, divides the pin 40 into a first portion 56
and a second
portion 58. The first portion 56 is designed to extend into the mold cavity
60, when the mold
castings 42, 42' (the casting 42' is correspondingly configured with respect
to the casting 42), are
combined, to form the mold 43. When the castings 42, 42' (casting 42' is
similar to the casting 20'
above) are combined, they (the inner surfaces 42a, 42a' of the respective
castings 42, 42') define the
mold cavity 60 in the shape of the desired part, as shown in Fig. 7.
Additionally, the first portion 56
of the pin 40 may be tapered outward, in a direction toward the collar 46, if
desired.
The second portion 58 is threaded, along at least a portion 58a of it. The
second portion 58
attaches in a screw-like manner to the bore 47, that is correspondingly
threaded (along a portion 47a
of it), in the protrusion 44. While this screw-like arrangement for pin 40 at
its second portion 58,
for retention in the bore 47 is preferred, other retention arrangements for
the pin 40 and
configurations of the second portion 58 of the pin 40 for engagement and
retention in the bore 47
are also permissible.
The pins 40 are releasable as a single unit, so that when a pin 40 needs to be
replaced, it can
be unscrewed from the protrusion 44, and replaced with another pin 40. The
replacement pin, upon
its installation, will be in a straight alignment.
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The pin 40 is preferably a single piece unitary member, typically formed by
conventional
metal working techniques and processes. The pin 40 is, for example, made of
materials such as
steel, for use with an aluminum casting 42 (the aluminum casting 42 including
the protrusion 44
that a forms a part of the boss 45). The collar 46 (that forms the other part
of the boss 45) is
typically torroidal in shape (and for example, of a circular cross-section)
and of a height or
longitudinal dimension "y" that is, for example, at least approximately half
of the protruding height
"x" of the boss 22 of the conventional casting 20, as shown in Fig. 2.
Accordingly, the protrusion
44 of the boss 45 is of a height (longitudinal dimension) "z" from the surface
42a of the casting 42,
this height "z" forming the other half of the height (longitudinal
dimension)"x", the total height of
the boss 45, as shown in Fig. S. Alternately, for example, depending on the
mold used, the height of
the boss 45, can be any desired height, defined by the height (longitudinal
dimension) of the
protrusion 44 plus the longitudinal dimension of the collar 46 of the pin 40.
The collar 46, extends laterally along a transverse axis 65 (the transverse
axis 65 is
perpendicular to the longitudinal axis 55). The collar 46 is typically of a
configuration
corresponding to that of the protrusion 44, with its periphery 46a typically
coincident or flush with
the periphery (peripheral surface) 44a of the protrusion 44. The collar 46
also includes first 46b and
second 46c surfaces on its upper 66 and lower 67 sides respectively (in a
typical orientation). The
collar 46 serves as a stop surface for the pin 40, limiting its travel (by the
second portion 58 of the
pin 40) into the bore 47 of the protrusion 44.
Fig. 8 shows a part or product 70 produced by a rotational molding process
using a mold 43
formed from the castings 42 and 42', as shown in Fig. 7. The part or product
70 includes openings
72 defined by the pins 40, as they were positioned in the mold cavity 60 (Fig.
7).
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An exemplary operation, using a mold 43 of the present invention, formed from
the castings
42 and 42' with the pins 40 in the casting 42 (the corresponding and matching
casting 42' typically
does not accommodate pins 40), is now detailed. This exemplary operation
employing the mold 43,
may be used for making a part or product similar to the part or product 70. In
this exemplary
operation, reference is made to Figs. 4-8. This exemplary operation is
conducted in accordance with
standard rotational molding industry practice, except where noted below.
Initially, corresponding castings 42, 42' are placed onto racks, similar to
racks 38 and 38' of
Figs. 3A and 3B respectively. The racks 38, 38' are joined to define a rack
unit for processing in a
rotational molding machine. By joining the racks 38, 38', the corresponding
castings 42, 42' are
coupled together to form molds 43, with cavities 60, therein. The cavity 60
is, for example,
configured in the shape of the part or product 70.
Polymer powder, such as micro-pelletized or microsphered high density
polyethylene
(HDPE), with pellet sizes ranging from approximately 0.0165-0.0360 inches, one
such powder, for
example, Esso 8760, available from Esso Chemical Company of Canada (in powder
form, or
micropelletized or microsphered as above), at approximately .230 to .270 grams
(for example, .250
grams is preferred), is loaded (or placed) into the cavity 60 of each mold 43.
The rack units holding
the molds 43 are then processed by McNeil 800 (fornierly known as a McNeil-
Akron Roto-CastT'"
800) rotational molding machine (apparatus), commercially available from Ferry
Industries, Inc. of
Stow, Ohio, USA.
The molds 43 (as held in the respective rack units) are heated and
simultaneously rotated, at
speeds of approximately 6 revolutions per minute (rpm) for the inner drive
rotation and 7.5 rpm for
the outer drive rotation, of the rotational molding machine (apparatus)
(McNeil 800 rotational
molding machine). The heating, coupled with the rotation, allows the polymer
powder to impinge
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on all internal surfaces of the mold 43 (these internal surfaces including,
the surfaces 42a, 42a' of
the respective castings 42, 42', as shown in Fig. 7, and the surface 44a of
the casting 42), to form a
fused layer, typically of uniform thickness. Temperatures inside the cavity
60, may be, for
example, approximately 560-600°F, and cycle times are approximately 14-
17 minutes.
The molds 43 are cooled while rotating, so that the plastic skin solidifies.
Cooling may be
by forced cold air or water spray. Once sufficiently cool, the rack units are
separated into the
component racks 38, 38' allowing the molds 43 to be opened, and the parts 70
removed.
While rotational molds and methods for use thereof have been shown and
described above,
the present invention can easily be modified by those skilled in the art so as
to be used in other
molds and methods for use, such as injection molds, blow molds, and the like.
There have been shown and described apparatus and components of preferred
embodiments
for rotational molding. It is apparent to those skilled in the art, however,
that many changes,
variations, modifications, and other uses and applications for the above
described embodiments are
possible, and also such changes, variations, modifications, and other uses and
applications which do
I S not depart from the spirit and scope of the invention are deemed to be
covered by the invention,
which is limited only by the claims which follow.
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